The present invention is related to an aluminum alloy having an improved workability and mechanical characteristics such as shear cutting ability, a high strength and a high abrasion resistance. The present invention is also related to a method for making the above-mentioned alloy. The alloy provided by the present invention has characteristics suitable for plastic working and for being used for cylinder sleeves and pistons in internal combustion engines and for guide cylinders for guiding magnetic tapes in video tape recorders (VTRs), for example.
Aluminum alloys containing a certain amount of silicon therein, that is an aluminum-silicon alloy, are being used for pistons of internal combustion engines and guide rollers in VTRs. Some of the examples of such alloys are named AC8A (AA336), AC8B and AC8C (AA332) which are used for casting, ADC12 (A383, A384) used for die casting, and A4032 used for wrought and forging. In general, aluminum-silicon alloys have common characteristics such as high temperature strength, high abrasion resistance and high corrosion resistance. But the characteristics are modifiable, according to the requisitions required to the alloy in various cases, by varying the composition, manufacturing process and heat treatment thereof. That is, one of the above characters may be emphasized by suitably determining the composition. For example, alloy A4032 has a superior mechanical strength and abrasion resistance at high temperatures and small coefficient of thermal expansion. When processing the alloy A4032 which is smaller than 100 mm in diameter, for example, raw material is extruded and cut out by a sawing machine for further processing.
Requirement for a raw material is determined by the characteristics required in relation to a final product. But it is also required or necessary that the raw material has the characteristics which enable and facilitate processing thereon while processing it to make the final product. The characteristics required in relation to the processing thereof are plastic workability, working ability and shear cutting ability. Shear cutting ability is important to simplify the process because cutting by shear is much simpler than cutting by a lathe machine, for example. The effects of this simplification become even stronger in a mass production. But, because the shear cutting ability is contradictory to ductility and toughness of the material, it was difficult to obtain an aluminum-silicon alloy having both a good shear cutting ability and such mechanical characteristics as ductility and toughness. For example, when the alloy A4032 is cut by shear, cracks appear in the cut surface and the surface becomes rough, and the product is not suitable for forging. On the other hand, because the alloy A4032 does not have a high fatigue strength, the alloy is not suitably used in pistons and connecting rods. As typically seen in the alloy A4032, an aluminum-silicon alloy having a high abrasion resistance, stress-corrosion resistance, strength at high temperatures, fatigue resistance and shear cutting ability has not been provided by now.